The invention relates to a circuit for widening the stereobase in the reproduction of stereophonic sound signals, including one amplifier each for stereo signals assigned to the right-hand and left-hand channel, each amplifier comprising a non-inverting input for the corresponding stereo signal and an inverting input for an output signal fed back via a resistor from the amplifier output, and an ON/OFF connection between the inverting inputs of both amplifiers.
Portable sound reproducing instruments despite increasing miniaturization are required to satisfy all requirements as to reproduction quality at least as regards the electronic signal processing. Due to the small dimensions of these instruments the spacing between the loudspeakers to which the signals of the right-hand channel and left-hand channel are applied for the reproduction of stereophonic sound signals, however, becomes so small that the stereophonic effect is seriously degraded, good stereophonic reproduction necessitating a relatively large spacing between the loudspeakers. Proposals have thus been made to achieve a virtual increase in the spacing of the loudspeakers, the so-called stereobase, by influencing the signals applied to the loudspeakers.
Known from DE 39 14 681 C2 is a circuit assembly of the aforementioned kind with the aid of which the stereobase can be widened virtually so that despite a small spacing of the loudspeakers the spatial sound impression is improved. In this known circuit assembly a switch formed by a field-effect transistor and a filter are provided in the connection of the inverting inputs of the amplifiers assigned to the two channels. Using a field-effect transistor as the switch in the connection of the inverting inputs necessitates generating a control voltage for this field-effect transistor when the usual electronic components of the circuit assembly are equipped with advanced devices making do with low supply voltages of, for example, lower than 3 V. Apart from this it is a nuisance having to provide a switch in the connection via which the sound signals are communicated.
An objective of the invention is to configure a circuit assembly of the aforementioned kind so that it can be put to use even at low supply voltages. Further, an objective is to achieve an ON/OFF base widening effect without a switch being needed in the connection via which the sound signals are communicated.
An embodiment of the invention includes a pair of amplifiers for stereophonic sound signals with a connection between the inverting inputs of the two amplifiers formed by two amplifiers connected in antiparallel as voltage followers and a second resistor connected in series with the output of each amplifier. Further, in another embodiment, a blocking input by which the amplifiers can be switched to an inactive state on application of a blocking signal in which they communicate no signal to their output.
The circuit in accordance with the invention permits widening the stereobase by simple ways and means whereby signaling the widening effect ON/OFF is possible without degrading the sound signals, the widening extent being influenced very simply by the selection of passive devices.